nice! funny this was one of the first that appeared for me, i also made a platformer.
after some time the jump sound effects stopped playing, and i kept getting stuck when growing in too small areas. i tried preventing that with a collision check in each direction that prevents growth when top&bottom or left&right are colliding.
nice graphics&music choice and nice polishing, although the camera "zooming" when moving while in small form is a bit disorienting at times.
also good job with introducing the mechanics at a slow pace.
i'd prefer if space was jumping and a different key was resizing, but cool game nonetheless